A large anisotropy of the electron distribution function in plasma production with prepulse-controlled high power KrF laser

A large anisotropy of the electron distribution function (EDF) was observed in high density plasma. The plasma was created by a 2-ps TW KrF laser system in which a prepulse energy was well controlled with a saturable absorber. The observed electron density at the emission area with He-like F ions was 0.7–1.5×1022 cm−3. A 90° deflection time by electron-ion collisions was calculated to be two orders of magnitude smaller than the laser pulse duration. Even with this high collisionality, the anisotropy of EDF was driven by the laser field and was maintained. That means the anisotropy will become a parameter instead of temperature in the high density plasma which was far from the equilibrium state. The energy transfer process will be discussed with these new measurements in future.